Photodetection devices may use complicated architecture based on a high doping and high operational electric field and voltage. A charge region may form part of a vertically arranged serial transition layer structure using a very high breakdown voltage resulting in high operational voltage use. Furthermore, the various layers of the serial structure are associated with being defined and controlled very precisely, resulting in a need for particularized doping or other techniques to obtain a viable structure.
An avalanche photodiode is a highly sensitive photodetector which has internal gain through avalanche multiplication. Avalanche photodiodes have been traditionally used for long haul optical communications; for a given data transfer rate, they can provide 10× better sensitivities than a PIN diode, for example. APDs can use normal incident light and can use a waveguide structure to couple incident light. For materials with lower absorption efficiency, such as Ge or quantum dots etc., a long absorption length/size may be needed to provide sufficient quantum efficiency. As a result of the long length/large size, traditional APDs may be bulky and have high dark current, low quantum efficiency, and low bandwidth. Additionally, large device size and high power consumption can be particularly detrimental for on-chip optical interconnect applications. Furthermore, traditional APDs may use separate absorption charge multiplication (SACM) design, which may result in high breakdown voltage (typically >25V for GeSi APDs) due to the serial placement of each region.